In various race settings, a racer can obtain an advantage by racing closely behind another racer. This advantage is caused by the leading racer's causing a disturbance in the air. The following rider generally will experience less drag by racing in the disturbed air created by the leading racer. Therefore, the following racer will exert less energy and effort by traveling in the disturbed air. Traveling in the disturbed air caused by another racer is called drafting.
Because of this advantage gained by drafting, various races have various rules regarding how long a following racer may travel within a given distance behind another racer. For example, in the biking portion of a triathlon, riders can only race within a given distance behind and within lateral distance to the side of a leading racer for a particular amount of time for a penalty is assessed against the drafting rider. Accurately assessing such penalties is difficult in a bicycle race setting, however, because judges cannot be effectively placed to cover an entire race course in a typical event.